The invention relates to an apparatus for reducing the nitrogen oxides in the exhaust gas of an internal combustion engine by adsorption of the nitrogen oxides and their subsequent desorption and conversion to nitrogen and oxygen.
Such a method and apparatus are known from Japanese Patent Application 91-135417. As disclosed therein the exhaust gases emitted by the internal combustion engine are passed through an adsorbent in the exhaust manifold which contains a zeolite for the retention of the nitrogen oxides. Nitrogen oxides stored in the zeolite by adsorption are subsequently separated from the adsorption element by desorption with the aid of low-oxygen exhaust gas heated in a hot-gas generator and are fed to a reduction catalytic converter in which the nitrogen oxides react to form nitrogen and oxygen.
One disadvantage is that the internal combustion engine is restricted to a specific mode of operation by the reduction catalytic converter.
Another known method for the post-engine reduction of NOx is the SCR process (selective catalytic reduction) in which a reducing agent is required.
It is the principal object of the present invention to provide a method of reducing nitrogen oxides which does not require additional reducing agents and which can be used without restriction in the entire operating range of the internal combustion engine.